分子结构对聚酰亚胺膜分离CO_2/CH_4性能的影响

气体在致密高分子膜中的渗透过程与高分子的链段活动性和自由体积有关,高分子的链段活动性越大,气体的扩散越容易,气体的透过速度越快,高分子自由体积增大,气体的溶解系数增大,扩散速率加快,透气速率上升．因此,为了得到高选择性和高透气性的分离膜,可对其化学结...     

Effects of charge density and hydrophobicity of ionene polymer on cell binding and viability

The binding of cationic ionenes onto budding protoplast was investigated and the results were associated with the cell viability. There are critical numbers of carbon atoms to induce effective cell disruption and cell binding. The longer the alkyl chain of the ionene, the lower the concentration at which cell disruption occurs. The ionenes with increased charge density undergo effective binding, while almost 2 orders of magnitude higher concentration are required for effective cell disruption. These results were associated with the cooperativity of the binding process, which induces local stress and solubilization of the lipid membrane. Received: 26 October 1999 Accepted: 23 March 2000     

铂(Ⅱ)配合物跨人红细胞膜传递的动力学研究

顺铂(cis-DDP)和顺式1,1-环丁烷二羧基二胺合铂(Ⅱ)(即卡铂,CBDCA)具有良好的抗癌活性,其主要靶分子均为DNA。但这些配合物与DNA作用前必须首先通过细胞膜。离体肿瘤对顺铂的摄入要比卡铂快得多,海拉细胞(Helas-3)摄入顺铂的速度要比摄入K_2PtCl_4或K_2PtCl_6慢。Binks等研究了鼠小肠摄取顺铂和卡铂的动力学机理,指出这两种配合物     

分析化学中的溶剂萃取技术

综述了近年来溶剂萃取在分析化学中应用的发展趋势。对溶剂萃取所发展的超临界流体萃取、固相萃取、固相微萃取及膜萃取方面作了重点叙述。引用文献35篇。     

一种静电驱动微机械变形反射镜

 以ANSYS软件的有限元分析为依据对变形反射镜结构模型进行研究,探讨各主要结构参数及驱动电压对变形位移的影响。考虑静电驱动力、张力和空气阻尼衰减对变形镜回复过程的影响,建立一种复合参数模型来预测变形镜的瞬态行为。结果表明,驱动器的弹性薄板厚度、跨度和电极间距明显影响变形位移;驱动器的变形位移随驱动电压的增加出现稳定的非线性增加和不稳定的“拉入”现象;驱动电压撤除后镜面回复时间短,重复性好。     

Membrane Extraction Combined with Thermodesorption/Gas Chromatography and Mass Selective Detection for the Analysis of Volatile Organic Compounds in Water

The range of application of a commercial thermodesorption-cryofocussing unit connected to a gas chromatograph/mass selective detector was extended to water analysis by using it in conjunction with membrane extraction. A flow of nitrogen passes through a silicone hollow fiber immersed in the water sample and extracted volatile organic compounds are enriched in a sorption tube mounted on top of the extraction cell. The sorption tube is then placed in the thermodesorption unit and analyzed by GC/MS. The optimal extraction parameters of this combined method were found to be 30 min extraction at 20°C with a stirring speed of 1,250 rpm and a flow rate of 100 mL/min nitrogen using a silicone hollow fiber of 0.3 m length. Under these conditions the reproducibility of the method was 5.2–10.5% RSD. The linear dynamic range of the optimized method spans three orders of magnitude and detection limits were found to be 0.02–0.1 μg/L for cis/trans-1,2-dichloroethene, benzene, trichloroethene, chlorobenzene, bromobenzene, ethylbenzene, 1,1,2,2-tetrachloroethane, and 1,2/1,4-dichlorobenzene. The method was found to be suitable for compounds with boiling points up to 220°C as memory effects increased considerably from dichloro- to hexachlorobenzene. Highly contaminated groundwater samples were analyzed. Quantitative results corresponded well with those achieved with conventional headspace-GC/FID.     

X-Ray Structure of Bacteriorhodopsin at 2.5 Å Resolution

Microfocussed X-rays produced by an electron synchrotron were essential for the first structure elucidation of protein crystals having extremely small dimensions (5×20–40 μm). A further prerequisite for the successful crystal structure analysis of bacteriorhodopsin was a novel crystallization method using a lipid matrix. These methodological breakthroughs pave the way for further advances in structure determinations of membrane proteins.     

Electrospun fibrous membranes of poly (lactic-co-glycolic acid) with β-tricalcium phosphate for guided bone regeneration application

Guided bone regeneration (GBR) have been proved great success for the treatment of bone defects in oral implantology. Bone defects are reconstructed by the use of a barrier membrane which prevents the invasion of soft tissue and create a space for guiding new bone growth into the bone defect. To develop GBR membranes with higher bioactivity, poly (lactic-co-glycolic acid) (PLGA) fibrous membranes containing β-tricalcium phosphate (β-TCP) were fabricated via electrospinning. The presence of 5 wt% and 10 wt% of β-TCP in the fibers improved mechanical properties. In vitro biocompatibility results have shown that all membranes are non-cytotoxic and the presence of β-TCP increased cell adhesion and proliferation. Furthermore, cell viability results demonstrated that the presence of 5 wt% β-TCP is advantageous for osteoblast proliferation. Therefore, the results suggest that PLGA with 5 wt% β-TCP fibrous membranes meet the requirement of morphological, physical, mechanical and bioactive properties for an effective GBR membrane.     

Membranes based on non-synthetic (natural) polymers for wastewater treatment

During the last decades, rising environmental concerns about the widespread usage of petroleum-based synthetic polymers has caused naturally occurring polymers to gain momentous. As a biocompatible and environmentally friendly alternative, bio-based polymers are continuously gaining new domains of application in drug delivery systems, tissue engineering, membrane technology, bio-sensor devices, etc. There is an increasing number of scientists who have applied various kinds of biopolymers, such as cellulose, chitin, starch, and alginate to fabricate fully or semi-biodegradable membranes for wastewater treatment. Beside biocompatibility, biopolymers combine many attractive features such as hydrophilicity and functionalizability that makes them great candidates to enhance the performance of composite membranes to effectively purify water from hazardous pollutants. On the other hand, elevating thermo-mechanical and chemical stability of these bio-based materials by introducing new organic and inorganic additives is another main focus area. This review is concerned with 1) introducing the promising feature of biopolymers that can be used as a raw material to synthesize membranes for water treatment, 2) proposing a comprehensive categorization of these membranes based on their structure, and 3) discussing the performance of these membranes in eliminating various kinds of contaminants from effluents and their strength and weakness points.     

Direct contact ultrasound for fouling control and flux enhancement in air-gap membrane distillation

Air Gap Membrane distillation (AGMD) is a thermally driven separation process capable of treating challenging water types, but its low productivity is a major drawback. Membrane fouling is a common problem in many membrane treatment systems, which exacerbates AGMD’s low overall productivity. In this study, we investigated the direct application of low-power ultrasound (8–23 W), as an in-line cleaning and performance boosting technique for AGMD. Two different highly saline feedwaters, namely natural groundwater (3970 μS/cm) and RO reject stream water (12760 μS/cm) were treated using Polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) membranes. Theoretical calculations and experimental investigations are presented, showing that the applied ultrasonic power range only produced acoustic streaming effects that enhanced cleaning and mass transfer. Attenuated Total Reflection Fourier-Transform Infrared Spectroscopy (ATR FT-IR) analysis showed that ultrasound was capable of effectively removing silica and calcium scaling. Ultrasound application on a fouled membrane resulted in a 100% increase in the permeate flux. Cleaning effects accounted for around 30–50% of this increase and the remainder was attributed to mass transfer improvements. Contaminant rejection percentages were consistently high for all treatments (>99%), indicating that ultrasound did not deteriorate the membrane structure. Scanning Electron Microscopy (SEM) analysis of the membrane surface was used to confirm this observation. The images of the membrane surface demonstrated that ultrasound successfully cleaned the previously fouled membrane, with no signs of structural damage. The results of this study highlight the efficient and effective application of direct low power ultrasound for improving AGMD performance.